Recent E. coli Outbreaks - What can we learn from them

Updated: Nov 27, 2020

The latest outbreak

Ever since E. coli O157 H7 was discovered, the Center for Diseases Control or CDC has been constantly monitoring outbreaks of this bacterium. The latest outbreak happened last November 18, 2019; 17 people were infected. Through the use of Whole Genome Sequencing or WGS, it was confirmed that the outbreak was definitely caused by E. coli O157 H7. Samples taken from patients yielded genomic sequences that were very similar to the genomic sequences of the E. coli bacterium that was isolated from an unopened package of ‘Ready Pac Bistro® Chicken Caesar Salad’ which were found in the patient’s home. The Food and Drug Administration were able to identify farms within Salinas, California which could have been the source of the contaminated vegetables. Furthermore, investigators noted that some of those who were infected with E. coli O157 H7 did not eat Ready Pac Bistro® Chicken Caesar Salad which means this is not the source of the infection.1

Three days later, a recall of lettuce products with the same lot number was issued. The Maryland Department of Health discovered that these lettuces were contaminated with E. coli O157 H7. Additionally, the department also discovered that these were the lettuces used in the salad ‘Ready Pac Bistro® Chicken Caesar Salad’.1

Last November 22, 2019, further genomic analysis of the E. coli O157 H7 bacteria which were isolated from the patients showed that it is very similar to the E. coli O157 H7 bacteria that caused outbreaks in the Fall of 2017 and 2018 affecting both the United States and Canada. Interestingly, the aforementioned past outbreaks were also associated with the consumption of leafy greens and romaine.1

About a month later, while the Food and Drug Administration were still trying to pinpoint the origin of the outbreak, two more outbreaks occurred. In Canada, the outbreak was linked to the consumption of ‘Fresh Express Sunflower Crisp Chopped Salad Kits’. Fortunately, the investigators were finally able to trace back the outbreak to a common grower in Salinas.1

On January 15, 2020, the Center of Diseases Control and the Food and Drug Administration reported a total of 188 cases. No new cases were reported afterwards and the authorities declared that the outbreak had ended. Despite this, the investigations surrounding the outbreak continued.1

Investigations regarding the November 2019 outbreak concluded on May 21, 2020. In their final report, the Food and Drug Administration determined that the three outbreaks were actually caused by distinctly different strains of E. coli O157 H7. The main outbreak which occurred in November was associated with the consumption of two different brands of fresh-cut salads containing contaminated romaine lettuce. The same strain of E. coli O157 H7 was isolated from the faecal-soil composite samples taken from a public land used for cow grazing. This plot of land is situated a few miles upslope from the farm which produced the contaminated lettuce.2

In the end, the Food and Drug Administration was not able to determine a definitive source or route of contamination of the romaine fields. Their best guess was that the public land used for cow grazing may have been the main source of E. coli O157 H7. The field growing romaine was contaminated indirectly through the action of water run-off, wind, animals or vehicles which carried contaminated soil from the public land to the romaine field. After the investigations have concluded up until now, the FDA has been monitoring the Salinas region with the hopes of preventing future outbreaks.2

2020 Leafy Greens STEC Action Plan

The main problem with most leafy greens is that they are grown outdoors. Due to this, they are susceptible to contamination. Aside from this, they are often consumed raw. Cooking may eliminate any bacteria present in the vegetable but most consumers would choose to eat them raw because the process of cooking may negatively affect the health-associated properties of the vegetable. Due to these issues, the Food and Drug Administration has devised an action plan to minimize the occurrence of leafy-greens-associated E. coli outbreaks.3

Agricultural Water Safety

In the light of recent outbreaks, investigators observed that irrigation and other methods of watering the crops seem to be a major contributing factor to contamination. One action plan which was suggested to resolve this issue involves the usage of antimicrobial products designed specifically for treating irrigation water. While this suggestion is still up for approval, growers are advised to follow good agricultural practices when it comes to handling their water sources.3

Adjacent and Nearby Land Use

In the recent outbreak, investigators concluded that the romaine fields were contaminated with E. coli O157 H7 indirectly from nearby public land. The cows that grazed there may have shed E. coli O157 H7 to the soil in the public land. Rain, wind, animals, or vehicles may have brought the contaminated soil from this public land to the romaine fields. That is why it has been proposed that awareness campaigns about the responsible usage of lands that are near agricultural land should be promoted.3

Leafy Green Data Trust

Data regarding outbreaks must be made readily available for the government and those who are involved with the agriculture industry. This way both parties would be well informed and may be more involved in preventing them. So it has been proposed that a voluntary public-private data trust for leafy greens must be created.3

Improving Sampling Protocols

The agricultural community has come to the conclusion that their surveillance and sampling methods need to be improved. New knowledge and technologies aimed at improving their ability to know what to sample, when to sample, where to sample, and how often to sample is needed. Until the scientific community is able to come up with a better way of predicting outbreaks. California’s Central Coast, Central Valley and Imperial Valley, and Arizona’s Yuma would be monitored with vigilance.3

Improving the traceability of contaminated food

Detecting outbreaks is easy. Health workers would alert the authorities in situations wherein there is an unusually high number of cases of a disease occurring within a short span of time. Determining the causative agent of the outbreak is also straightforward as there are established methodologies on how to do this. The difficult part when it comes to handling outbreaks is tracing it back to its source. This step is important in ending the outbreak fast. Once the source is determined, appropriate action could be taken to eliminate the source and prevent new cases from occurring. Unfortunately, the supply chain of leafy vegetables is still archaic. Technologies are still not embedded in the supply chain enough to achieve thorough traceability from source to consumer. That is why upgrades to the supply chain which aims to modernize the traceability of the food items through technology have been proposed.3

Shopper Card Data

Knowing what an outbreak-patient bought before the onset of their symptoms is valuable for investigators. When multiple outbreak-patients purchased a common product, then there is a huge chance that the common product is the source. Knowing what a person purchased around the time of the outbreak is referred to as point-of-purchase record-keeping. This kind of record-keeping is made available only if people would utilize shopper cards. Most established grocery stores utilize shopper cards or loyalty cards. However, a shopper’s purchase history is not readily accessible to the authorities.3

Improving Whole-Genome Sequencing Database

Genomic databases like the National Center for Biotechnology Information are already operational. However, they would benefit greatly if new data is constantly being shared through this database. This way when Whole Genome Sequencing is done in a certain area, they would have access to Genome Sequences collected from a huge network of laboratories.3

Improving Communications during Outbreaks

One important aspect of managing outbreaks is communication. Health workers who are tasked with taking care of outbreak patients must report outbreaks to the authorities immediately as they are first to know. Once the source of the infection is known, the authorities must inform the appropriate individuals or companies swiftly; maybe order them to recall their products. All of these must be conducted with haste so that an appropriate response would be made. Due to these, a review of the current inter-agency communication systems has been proposed.3





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